Error map
NamespaceNotFound: ns not found MongoServerError: ns not found (NamespaceNotFound) — dropping/renaming/collStats on a missing collection
MongoDB · layer 5, Data
Centre: this error. First ring: errors it is linked with (9). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (9)
MongoDB: MongoServerError: Document failed validation (code 121)
The collection has a JSON Schema validator and the inserted/updated document doesn’t satisfy it.
RuntimeError: dictionary changed size during iteration
A dict (or set) was modified while being looped over.
TypeError: unhashable type: 'list'
A mutable object (list, dict, set) was used as a dict key or set member.
MongoServerError: bad auth : Authentication failed. (Atlas user / special characters in password)
Atlas rejected the username/password in the connection string.
MongoServerError: Exceeded memory limit for $group, but didn't allow external sort. Pass allowDiskUse:true to opt in
An aggregation stage needed more than 100 MB of RAM and spilling to disk wasn't enabled.
MongoServerError: BSONObj size: 17825792 (0x1100000) is invalid. Size must be between 0 and 16793600(16MB)
A single document (or an aggregation result row) grew past MongoDB's 16 MB limit.
Mongoose: OverwriteModelError: Cannot overwrite `User` model once compiled.
`mongoose.model('User', schema)` was called twice with the same name, typically from hot reloading.
Mongoose: MissingSchemaError: Schema hasn't been registered for model "User". Use mongoose.model(name, schema)
You used `populate()`/`ref` for a model that hasn't been registered yet.
MongoServerError: Collection db.users already exists (NamespaceExists)
`createCollection` (or an index/rename) targeted a name that is already in use.
Two steps away (25)
MySQL ERROR 1146 (42S02): Table 'db.table' doesn't exist
The query references a table that MySQL can’t find in that database.
MySQL ERROR 1054 (42S22): Unknown column in 'field list'
The query references a column that doesn’t exist in the table (or an unquoted string being read as a column).
PostgreSQL: ERROR: relation "x" does not exist
The table/view isn’t found — missing migration, wrong schema, or a case-sensitive quoted name.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
java.util.ConcurrentModificationException
A collection was modified while being iterated (even in a single thread).
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)
Code tried to modify an immutable or fixed-size collection.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
TypeError: unsupported operand type(s) for +: 'int' and 'str'
An operator was used between two incompatible types, such as adding a number to a string.
TypeError: can only concatenate str (not "int") to str
You joined a string and a non-string with +.
MongooseError: Operation `users.find()` buffering timed out after 10000ms
Mongoose queued a query waiting for a connection that never opened.
MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
The MongoDB driver couldn’t find a reachable server for the connection string.
MongoServerError: E11000 duplicate key error collection: db.users index: email_1 dup key
An insert/update violated a unique index in MongoDB.
Kubernetes: OOMKilled (exit code 137)
The container used more memory than its limit, and the kernel killed it.
Segmentation fault (core dumped)
A program accessed memory it wasn’t allowed to, and the kernel killed it with SIGSEGV (exit code 139).
Killed / Out of memory: Killed process (Linux OOM killer)
The kernel ran out of memory and killed a process to recover — the program just prints “Killed” (exit code 137).
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
CastError: Cast to ObjectId failed for value "x" (type string) at path "_id"
A value that isn’t a valid 24-hex-character ObjectId was used in an _id query.
ValidationError: User validation failed: email: Path `email` is required.
A document failed Mongoose schema validation before saving.
Mongoose 6+: StrictPopulateError: Cannot populate path `author` because it is not in your schema
`populate('author')` references a field that isn't defined in the schema with a `ref`.
Mongoose: VersionError: No matching document found for id "5f..." version 3 modifiedPaths "items"
Mongoose tried to save a document whose array was changed by someone else since you loaded it (optimistic concurrency).
Mongoose: [MONGOOSE] DeprecationWarning: Mongoose: the strictQuery option will be switched back to false by default in Mongoose 7
A deprecation warning about how unknown fields in query filters are handled.
MongoParseError: option usenewurlparser is not supported
Old connection options removed in Mongoose 6 / driver 4 are still passed to `mongoose.connect`.
MongooseError: Model.find() no longer accepts a callback
Mongoose 7+ removed callback support from queries; they return promises.
Mongoose: CastError: Cast to date failed for value "abc" (type string) at path "createdAt"
A value couldn't be converted to the schema type at that path (date, number, boolean).
MongoServerSelectionError: Could not connect to any servers in your MongoDB Atlas cluster. One common reason is that you're trying to access the database from an IP that isn't whitelisted
Atlas rejects connections from IP addresses that aren't in the project's Network Access list.
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